[abstract] PERFORMANCE ASSESSMENT OF THE BIRD AVIAN VENTILATOR IN THE HYPERBARIC ENVIRONMENT

Abstract

BACKGROUND: The Bird Avian Ventilator (BAV), presently used by the USAF Emergency Medical Services as a transport ventilator, has recently been accepted for use on cargo aircraft for USAF aeromedical evacuation. Airway pressure, control settings, alarm parameters and power signals are continuously monitored by a microprocessor which offers a variety of ventilatory modes. The objective of this test was to evaluate the performance of the BAV in the hyperbaric environment. METHODS: The BAV was tested in the control mode of operation at 1 ATA, 2 ATA, 2.36 ATA and 3 ATA. An artifical lung simulator was set for testing two lung compliances: 0.10 L/cm H2O and 0.05 L/cm H2O. Required settings for using BAV in the control mode were: tidal volume (TV, ml), flow (l/min), and breath rate (bpm). Measured tidal volumes (TVm) were recorded at three depths and ten tidal volume settings (TVs = 200 to 2000, by 200 ml increments) using a 1:2 inspiratory/ expiratory test breath cycle ratio. Three independent measures of proximal airway pressure were determined from identical sites on the patient breathing circuit. Positive end expiratory pressure (PEEP) was not used in this test. The model fitting the data most satisfactorily was TVm = TVs x [a (a + ATA - 1)]fl. A nonlinear least squares program (SAS NLIN) was used to obtain estimates of a (0.880) and fl (0.554). Estmiates of flows were unaffected by increased ambient pressures, and no aberrant functioning was observed when compared to 1 ATA baseline performance checks. Initially, however, the membrane control switches became inoperative under increased atmospheric pressure and required venting. With the BAV in control mode during volume-cycled ventilation, our findings show this ventilator can provide safe and acceptable tidal volumes, in conjunction with proximal airway pressures and breath rate when exposed to hyperbaric pressures. CONCLUSION: A conversion table was developed to assist users in selecting corrected settings on the ventilator at the tested pressures listed above. This table will be presented and discussed.